[SYCL][Doc] Update to the test plan for free function kernels extension

[dyniols]

Updates based on feedback to the previous PR which has already been merged with test plan for free function kernels extension.

Changes done:

• moved check related to aliases into unit-tests category.
• added two new checks into e2e category related to treating free function kernel as device or host function.
• updated Interaction with additional kernel properties part.
• updated description for get_kernel_id what mean valid kernel identifier in context of unit-testing.
• most of changes were related to refactoring text into consistent column limit (which is 80) for markdown doc.

Previous PR: #17886
Docs: https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/proposed/sycl_ext_oneapi_free_function_kernels.asciidoc